This application relates to the art of controls and methods for operating electric water heaters. The invention is particularly applicable to a control apparatus and method that uses a control module running software for operation of a water heater. However, it will be appreciated that the invention has broader aspects and can be practiced in other forms.
An electric water heater energizes one or more heating elements located within the water heater tank to heat water. Electrical power to the heating elements is managed through the operation of a control module, which controls the opening and/or closing of electrical relays connected in series between a power source and the heating elements. The thermal energy generated by the heating elements dissipates in the water, thereby heating the water according to a desired or preset water temperature. The control module is operable to interrupt power to the heating elements, limiting the possibility that the water temperature will substantially exceed the desired temperature, by opening one or more of the electrical relays. However, certain circumstances may cause the heating elements to heat the water above the desired water temperature, resulting in a high temperature condition. For example, one or more of the relays may malfunction and/or fuse shut, limiting the ability of the control module to open and/or close the relays. If a relay fuses shut, the control module will not be able to open the relay and the heating elements will continue to heat the water.
It is known that one or more electric water heater components involved with the heating of the water may be designated as “critical” components. Electric water heater components are identified as critical components if failure of that particular component may directly result in a high temperature condition in the water heater. For example, if the failure of a relay would cause a high temperature condition, the relay is identified as a critical component. Critical components are more costly and have very high reliability requirements. It is desirable, therefore, to minimize the number of critical components in an electric water heater, which simultaneously minimizes the potential for a high temperature condition.